Wave motions in the sea and large lakes are a potential energy source which till now is very little utilized. The available wave energy depends on the wave height and is naturally different for different locations. The average wave energy during a year is dependent on the different wind conditions, which are highly influenced by the distance of the location from the nearest coast. Measurements have, among other things, been made in the North Sea. At a measuring point approx. 100 km to the west of the coast of Jutland where the depth was approx. 50 m, measurings of the wave height have been made.
In order to utilize the energy that is available by the motions of the sea waves, different types of wave power assemblies for the generation of electric power have been proposed. However, these have not succeeded to successfully compete with conventional electric power production. Wave power plants realized hitherto have in the main been test plants or used for local energy supply to navigation buoys. In order for commercial electricity production to be feasible, and thereby give access to the large energy reserve available in the motions of the sea waves, it is not only required that the setting out of the assemblies is carried out in suitably located places. It is also necessary that the assembly is reliable, has high efficiency as well as low manufacturing and operating costs.
Among the feasible principles of the conversion of wave motion energy to electric energy, a linear generator should in that connection to the largest extent meet these requirements.
The vertical motions of the hull caused by the wave motions can thereby directly be transferred to a reciprocating motion of the rotor of the generator. A linear generator may be made very robust and simple and by it being anchored at the bottom, it becomes solidly unaffectable by streams in the water. The only movable part of the generator will be the reciprocating rotor. By the few movable parts thereof and the simple constructive build-up thereof, the assembly becomes very reliable.
By, for instance, U.S. Pat. No. 6,020,653, a wave power assembly is previously known, which is based on the linear generator principle. Hence, the specification describes a generator anchored at the bottom, which generator produces electric energy from the wave motions of the sea surface. A generator coil is connected to a hull so that the coil moves up and down with the wave motions. A magnetic field acts on the coil when it moves so that an electromagnetic force is generated in the same. The magnetic field is such that it provides a uniform field having a single magnetic orientation along the length of stroke of the entire coil. The generator comprises a base plate on bottom of the sea that carries the magnetic core in which the coil moves.
Furthermore, a wave power assembly provided with a linear electric generator is previously known by U.S. Pat. No. 4,539,485. The rotor thereof consists of a number of permanent magnets and the winding of the generator is arranged in the surrounding stator.
Further, in PCT/SE02/02405, a wave power assembly is disclosed having a linear generator in which the rotor is permanent magnetic and the stator comprises winding forming a plurality of poles distributed in the direction of motion of the rotor.
It is important that the guiding of linear motion of the rotor in relation to the stator is exact and reliable so that the size of the gap between the rotor and stator is retained at an exact value. The gap is in the size of 1-5 mm, preferably about 2 mm. Since a generator of the type in question may be fairly large, insufficient precision in the guiding entails that the size of the gap risks deviating substantially from the predetermined one. This entails asymmetry of the occurring magnetic forces, which results in harmful asymmetric forces on the rotor with the risk of operational disturbances as well as breakdown. Also the electromagnetic transformation of energy is effected negatively by erroneous gap size.
Therefore, great demands are made that the rotor is well mounted in the cross direction, simultaneously great demands are made on the service life of the bearing mounting. An assembly of the kind in question is calculated to be in operation during a time of 30 years or more. Usual ball bearings normally have a service life that is considerably shorter than this. Exchange of bearings is very expensive since frequently the generator is located far out on the sea and at a large depth.
The object of the present invention is, against this background, that for a wave power assembly of the kind in question a bearing mounting of the rotor is provided which overcomes the problems mentioned and which accordingly is simple and reliable and which has a long service life.